chore: cleanup Config instantiation codepaths (#8226)

This PR does various types of cleanup before I can proceed with more
ambitious changes to config loading.

First, I noticed duplicated code across these two methods:


774bd9e432/codex-rs/core/src/config/mod.rs (L314-L324)


774bd9e432/codex-rs/core/src/config/mod.rs (L334-L344)

This has now been consolidated in
`load_config_as_toml_with_cli_overrides()`.

Further, I noticed that `Config::load_with_cli_overrides()` took two
similar arguments:


774bd9e432/codex-rs/core/src/config/mod.rs (L308-L311)

The difference between `cli_overrides` and `overrides` was not
immediately obvious to me. At first glance, it appears that one should
be able to be expressed in terms of the other, but it turns out that
some fields of `ConfigOverrides` (such as `cwd` and
`codex_linux_sandbox_exe`) are, by design, not configurable via a
`.toml` file or a command-line `--config` flag.

That said, I discovered that many callers of
`Config::load_with_cli_overrides()` were passing
`ConfigOverrides::default()` for `overrides`, so I created two separate
methods:

- `Config::load_with_cli_overrides(cli_overrides: Vec<(String,
TomlValue)>)`
- `Config::load_with_cli_overrides_and_harness_overrides(cli_overrides:
Vec<(String, TomlValue)>, harness_overrides: ConfigOverrides)`

The latter has a long name, as it is _not_ what should be used in the
common case, so the extra typing is designed to draw attention to this
fact. I tried to update the existing callsites to use the shorter name,
where possible.

Further, in the cases where `ConfigOverrides` is used, usually only a
limited subset of fields are actually set, so I updated the declarations
to leverage `..Default::default()` where possible.

codex-rs/cli/src/debug_sandbox.rs

@@ -109,7 +109,7 @@ async fn run_command_under_sandbox(
     log_denials: bool,
 ) -> anyhow::Result<()> {
     let sandbox_mode = create_sandbox_mode(full_auto);
-    let config = Config::load_with_cli_overrides(
+    let config = Config::load_with_cli_overrides_and_harness_overrides(
         config_overrides
             .parse_overrides()
             .map_err(anyhow::Error::msg)?,

codex-rs/cli/src/login.rs

@@ -6,7 +6,6 @@ use codex_core::auth::CLIENT_ID;
 use codex_core::auth::login_with_api_key;
 use codex_core::auth::logout;
 use codex_core::config::Config;
-use codex_core::config::ConfigOverrides;
 use codex_login::ServerOptions;
 use codex_login::run_device_code_login;
 use codex_login::run_login_server;
@@ -210,8 +209,7 @@ async fn load_config_or_exit(cli_config_overrides: CliConfigOverrides) -> Config
         }
     };
 
-    let config_overrides = ConfigOverrides::default();
-    match Config::load_with_cli_overrides(cli_overrides, config_overrides).await {
+    match Config::load_with_cli_overrides(cli_overrides).await {
         Ok(config) => config,
         Err(e) => {
             eprintln!("Error loading configuration: {e}");

codex-rs/cli/src/main.rs

@@ -631,7 +631,11 @@ async fn cli_main(codex_linux_sandbox_exe: Option<PathBuf>) -> anyhow::Result<()
                     ..Default::default()
                 };
 
-                let config = Config::load_with_cli_overrides(cli_kv_overrides, overrides).await?;
+                let config = Config::load_with_cli_overrides_and_harness_overrides(
+                    cli_kv_overrides,
+                    overrides,
+                )
+                .await?;
                 for def in codex_core::features::FEATURES.iter() {
                     let name = def.key;
                     let stage = stage_str(def.stage);

codex-rs/cli/src/mcp_cmd.rs

@@ -8,7 +8,6 @@ use clap::ArgGroup;
 use codex_common::CliConfigOverrides;
 use codex_common::format_env_display::format_env_display;
 use codex_core::config::Config;
-use codex_core::config::ConfigOverrides;
 use codex_core::config::edit::ConfigEditsBuilder;
 use codex_core::config::find_codex_home;
 use codex_core::config::load_global_mcp_servers;
@@ -200,7 +199,7 @@ async fn run_add(config_overrides: &CliConfigOverrides, add_args: AddArgs) -> Re
     let overrides = config_overrides
         .parse_overrides()
         .map_err(anyhow::Error::msg)?;
-    let config = Config::load_with_cli_overrides(overrides, ConfigOverrides::default())
+    let config = Config::load_with_cli_overrides(overrides)
         .await
         .context("failed to load configuration")?;
 
@@ -349,7 +348,7 @@ async fn run_login(config_overrides: &CliConfigOverrides, login_args: LoginArgs)
     let overrides = config_overrides
         .parse_overrides()
         .map_err(anyhow::Error::msg)?;
-    let config = Config::load_with_cli_overrides(overrides, ConfigOverrides::default())
+    let config = Config::load_with_cli_overrides(overrides)
         .await
         .context("failed to load configuration")?;
 
@@ -392,7 +391,7 @@ async fn run_logout(config_overrides: &CliConfigOverrides, logout_args: LogoutAr
     let overrides = config_overrides
         .parse_overrides()
         .map_err(anyhow::Error::msg)?;
-    let config = Config::load_with_cli_overrides(overrides, ConfigOverrides::default())
+    let config = Config::load_with_cli_overrides(overrides)
         .await
         .context("failed to load configuration")?;
 
@@ -421,7 +420,7 @@ async fn run_list(config_overrides: &CliConfigOverrides, list_args: ListArgs) ->
     let overrides = config_overrides
         .parse_overrides()
         .map_err(anyhow::Error::msg)?;
-    let config = Config::load_with_cli_overrides(overrides, ConfigOverrides::default())
+    let config = Config::load_with_cli_overrides(overrides)
         .await
         .context("failed to load configuration")?;
 
@@ -678,7 +677,7 @@ async fn run_get(config_overrides: &CliConfigOverrides, get_args: GetArgs) -> Re
     let overrides = config_overrides
         .parse_overrides()
         .map_err(anyhow::Error::msg)?;
-    let config = Config::load_with_cli_overrides(overrides, ConfigOverrides::default())
+    let config = Config::load_with_cli_overrides(overrides)
         .await
         .context("failed to load configuration")?;